The invention relates generally to an operating strategy for motor vehicles having part time or adaptive drive systems and more particularly to an operating strategy for motor vehicles having part-time or adaptive drive systems which activates the drive system clutch in certain operating conditions when the vehicle is heavily loaded.
The design of motor vehicles and motor vehicle drive line components routinely addresses worst case scenarios. Operation and handling of the vehicle when it is loaded to the maximum, operation and stability of the vehicle at maximum operating speeds, operation and cooling of the vehicle at a maximum design ambient temperature and operation and performance of the vehicle under maximum braking conditions are all familiar concerns of motor vehicle design and test engineers. For example, rear axles, rear differential gearing, particularly the hypoid gears of a differential, and the rear prop shaft in an adaptive four-wheel drive vehicle must all be designed to withstand maximum engine torque since the vehicle will most generally be operated in two-wheel drive.
While the vehicle must perform competently, satisfy numerous operating parameters under these extreme conditions and component parts must be designed to survive them, it is acknowledged that few vehicles are subjected to such operating maximums and fewer still for repeated events or extended periods of time. This observation suggests that operational modes may be developed which are activated or engage only during extreme operating conditions which may then reduce loading, fatigue and wear on parts subjected to such operating extremes, thereby permitting designs which are smaller and lighter but which still provide the appropriate load carrying capability and safety margins for extreme operating conditions.
The present invention is directed to a drive line operating strategy which provides improved vehicle operation and durability while allowing reductions in the size and hence weight of certain drive line components.
An apparatus and method of operating an adaptive drive system of a motor vehicle which reduces drive line wear, improves safety margins and permits weight reduction in drive line components, activates a clutch between a primary and secondary drive line in certain operating conditions when the vehicle is determined to be heavily loaded. Heavy vehicle loading is determined through data manipulation from sensors typically already available in a vehicle. The operating method may be added to programs or subroutines in an adaptive system controller and may operate automatically, i.e., without driver intervention.
The steps of the method include sensing the position of a throttle position sensor, sensing instantaneous speeds of a motor vehicle and computing instantaneous acceleration, determining whether the ratio of vehicle acceleration to throttle position is less than a predetermined threshold and engaging a transfer case clutch to transfer drive torque from a primary drive line to a secondary drive line.
Operation of this method is transparent to the driver inasmuch as the clutch is activated only when the vehicle is heavily loaded as determined by the acceleration to throttle position ratio. Once activated, the clutch preferably remains activated for the duration of an ignition cycle.
Operation of the motor vehicle drive line according to this method may be accompanied by a reduction in the size of various primary drive line components such as the differential hypoid gears, the primary drive shaft and the primary axles due to their reduced maximum torque loading thereby not only lowering their cost but also reducing the weight of the vehicle.
Thus it is an object of the present invention to provide an operating strategy for an adaptive drive system of a motor vehicle.
It is a further object of the present invention to provide an operating strategy for a transfer case clutch of adaptive drive system of a four-wheel drive motor vehicle.
It is a still further object of the present invention to provide an operating strategy for an adaptive drive system of a motor vehicle wherein acceleration and throttle position are detected and utilized to control engagement of an adaptive drive system clutch.
It is a still further object of the present invention to provide an operating strategy for an adaptive drive system of a motor vehicle through which heavy passenger and/or cargo loading of a motor vehicle may be determined by sensing acceleration and throttle position.
It is a still further object of the present invention to provide an operating strategy for an adaptive drive system of a motor vehicle which engages a drive line clutch during certain operating conditions upon a determination that the vehicle is heavily loaded.
Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended drawings wherein like reference numbers refer to the same component, element or feature.